Returns a set of previous time dimension members for calculation of cumulative sums.

## Syntax

` PreviousPeriods(Member_Expression)`

## Arguments

Member_Expression MDX expression that returns a member.

## Examples

`PreviousPeriods` returns optimized set of previous periods that can be used to aggregate some measure value for all previous time periods.

For example, `PreviousPeriods( [Time].[2015].[Q2 2015].[Jun 2015].[Jun 03 2015] )` will return a set:

```{
[Time].[2014],
[Time].[2015].[Q1 2015],
[Time].[2015].[Q2 2015].[Apr 2015], [Time].[2015].[Q2 2015].[May 2015],
[Time].[2015].[Q2 2015].[Jun 2015].[Jun 01 2015], [Time].[2015].[Q2 2015].[Jun 2015].[Jun 02 2015]
}```

which is all years until previous year (in this example Time dimension starts with year `2014`), all current year quarters until previous quarter (in this example `Q1 2015`), all current quarter months until the previous month (`Apr 2015` and `May 2015`) and all current month days until the previous day (`Jun 01 2015` and `Jun 02 2015`).

The following formula can be used to calculate a cumulative sum of invoice count until the previous period:

```Sum(
PreviousPeriods([Time].CurrentHierarchyMember),
[Measures].[Invoice count]
)```

If we want to calculate a cumulative sum of invoice count including the current period then we need to add the current period to the previous periods set:

```Sum(
{ PreviousPeriods([Time].CurrentHierarchyMember),
[Time].CurrentHierarchyMember },
[Measures].[Invoice count]
)```